This invention relates to vinylchloride resin compositions used for such food containers as blow-molded bottles and food packing materials including heat-shrinkable labels and heat-shrinkable sealing caps, and more specifically to those compositions that hardly become opaque even when treated with warm water.
Products made from vinyl chloride resins are cheap and excellent in mechanical properties, chemical resistance, weatherability and transparency, which allows for making products of optional hardness from hard to soft one by adding a wide variety of plasticizers, and are thus utilized in a wide field of applications. Since however, these resins are rather poor in thermal stability at the time of forming, it is considered that addition of stabilizers is essential. As these stabilizers, many types have been known such as a wide variety of metal containing compounds.
Non-toxic stabilizers that do not harm transparency have so far been adopted to vinyl chloride based resin compositions which are used for food containers and so forth. Of most frequent use are liquid composite stabilizers such as octyl tin mercaptide compound, octyl tin maleate compound, and calcium-soap/zinc-soap/auxiliaries (mainly epoxidized soybean oil, organic phosphorous acid compound).
It is well known, however that the vinyl chloride resin compositions so far used for bottles, among others, were problematical in that when these bottles were loaded with an aqueous solution of alcohol or carbonated beverage and then exposed to high temperature vapor for sterilization, or when the bottles themselves are kept under high temperature and high humidity atmosphere for a long time, the surface thereof becomes opaque thereby injuring the outer appearance. In the case where conventional vinyl chloride based resin compositions are formed into heat shrinkable labels to be adhered onto the bottles for carbonated beverages, they should be exposed to the sterilizing process as above, which makes them cloudy and harms their beauty.
As the result of our intensified researches and studies to eliminate such disadvantages as above, we eventually achieved this invention.